The present invention relates to a control cable, and more particularly, to a control cable in which a liner is to be prevented from shrinking, and operating feeling is good, and besides, the liner is not easily slipped out of an outer spring.
A control cable comprises a conduit and an inner core or inner cable, and is a means for remotely controlling an object to be controlled by pulling, by pushing and pulling or by rotating the inner cable.
The above-mentioned conduit generally comprises what is called an armour or outer spring and an outer coat. The outer spring is made by roll-forming a steel wire to a flat strip and then by winding in abutting convolutions to form a coiled spring. Another type of conduit comprises plural steel wires which are laid side by side and wound helically to form a tubular member. The outer coat is a layer of plastic materials which covers and protects the outside surface of the conduit.
The inner cable which is inserted into the above-mentioned conduit comprises a stranded wires obtained by twisting plural wires or strands which are mutually twisted.
In such a control cable, the inside surface of the above-mentioned outer spring is rubbed with the inner cable. Therefore, the operating efficiency and the durability are much influenced by coefficient of friction and degree of abrasion between the outer spring and the inner cable. Therefore, in some cases, as shown in FIG. 16, a tubular liner 3 is set at the inside surface of the outer spring 4 in order to reduce the friction and the abrasion. The tubular liner is generally made of plastics of which coefficient of friction is low and abrasion resistance is superior. The tubular liner can be closely set in the outer spring by winding a flat steel strip around the outside surface of the liner so that the liner is wrapped in the outer spring, or by inserting the liner into the conduit after the outer spring is formed in a coiled-shape.
By the way, recently temperature in an engine room or engine compartment of an automobile and so on has become much higher than the temperature heretofore. For example, it becomes 150.degree. C. under high temperature condition, and in a cold district, it might become -40.degree. C. Under the condition that environment temperature is so severe, troubles come out as mentioned hereinafter.
Under the condition that the above-mentioned control cable is closely contacted to the outer spring, if the control cable is heated, thermal expansion in the axial direction of the liner is restricted by the outer spring which has higher rigidity and lower coefficient of thermal expansion than the liner. Therefore, the liner cannot freely expand and release thermal stress thereof at high temperature. On the contrary, the liner can almost freely shrink when it is cooled. As a result of repeated rise and fall cycles of temperature, the liner shrinks successively and irreversibly in length.
In addition, when a liner is squeezed by the outer spring, the unevenness of the inside surface of the outer spring, especially at junctures of adjacent strips, comes out through the liner, therefore an operating feeling becomes worse, durability becomes lower, and so on.
Therefore, in order to reduce the above mentioned disadvantages, a clearance more than 0.5 mm between the control cable and the outer spring is required in a state that a liner is inserted into the outer spring. However, in this case, it is necessary to provide an additional mechanism so that the liner is not easy to slip out, for example, by making a flare portion at an end of the liner, or by putting a washer between the end of conduit and a member (e.g. cap member) to which the end of conduit is fixed.
On the other hand, with respect to the after-inserting type of conduit, even if there is a clearance between the liner and the outer spring, the liner cannot be easily inserted into the outer spring in case that a control cable is long.
The object of the present invention is to delete the above-mentioned disadvantages of the conventional control cable and to provide a control cable in which reversible thermal expansion and contraction of the liner is not hindered by the outer spring hence a liner is prevented from successive shrinking, the unevenness and roughness does not come out on the inside surface of the liner, and further, the liner is not easy to be slipped out of an outer spring without employing any special mechanism.